News
Thursday, 8 October 2009
Tree Sparrow Survey
You will, I know, be aware of the recent sad decline in the populations of both House and Tree Sparrows. However, you may not realise that here in the Croydon area we have what is probably the largest remaining breeding colony of Tree Sparrows in the UK right on our doorstep, at Beddington Farm. Over 900 young birds were fledged by 133 breeding pairs at this site in 2007, although the numbers have fallen back a little since. Unfortunately, the future is not especially rosy for the Beddington Tree Sparrow colony, or indeed for the Farm site itself - gravel extraction, followed by landfill, is causing a great deal of disturbance on the Farm and much of the topography is rapidly being altered. Although habitat restoration works will follow on progressively after the landfill, there is a fear that the sparrow colony could suddenly desert the site en masse in the meantime, as has occurred elsewhere in the country.
Concerned members of the Croydon RSPB Local Group, in conjunction with the Beddington Farm Bird Group and the landfill operator's own ecologist, sought guidance from the RSPB's regional staff on measures that might be taken to try to safeguard this very important Tree Sparrow colony. As a result, Ellie Burke (Agricultural Project Officer from RSPB's SE Regional Conservation Team) has produced a draft action plan. This includes survey work off the site to track and locate some of the considerable number of sparrows that leave the site during the post-breeding period each year. Where these birds actually go is a mystery as very, very few are reported outside the site boundary. It is possible that they may move a considerable distance away in their search for suitable food sources, and could even establish small breeding colonies elsewhere. Ellie has provided this background information:-
''Previous studies have shown that established tree sparrow colonies have a habit of waxing and waning. The Rutland Water colony has declined dramatically in recent years, in the face of little apparent change. However, the declines may be due to recent poor summers and the harsh winter. Tree sparrows in Leicestershire have also had a couple of below average breeding seasons, but the population has remained stable. It has been observed that, in naturally sustained populations, post-juvenile dispersal is the main source of emigration, but only 5% of chicks will actually recruit into other populations. First winter dispersal is generally only 5-10km, or until the birds find a reliable seed source or another wintering flock. Some birds have been known to travel much larger distances, but this is rare. Where small colonies do establish, they often have reduced breeding success and probably don't persist for long unless they regularly receive immigrants for the first few years.
"In the context of the Beddington population, the site is so isolated that juvenile recruitment into other populations seems unlikely. Finding a sufficiently large, reliable seed source in an urban environment is also difficult. In poor habitat and further from the established colony, tree sparrows are unlikely to persist, because low numbers of dispersing juveniles are less likely to find one another. Therefore, it seems the odds are stacked against any new breeding populations in a 5-10km radius of Beddington. In this case, it would be worth considering a wider area. However, this is not to say that there are no small populations establishing themselves around Beddington, and this is a key starting point in taking action to conserve them.''
It occurs to us that the network of RSPB Local Groups could provide a good spread of experienced observers for the kind of off-site survey that Ellie has proposed. To put that theory to the test, we invite any keen birders from groups within an arbitrary 20 km of Beddington, such as yours, to join us in searching for the missing Tree Sparrows, at least during the coming winter (i.e. from the beginning of October 2009 to the end of March 2010). The survey work envisaged is not at all onerous - all that is required of any participant is that he or she keeps an eye open for Tree Sparrows whilst out birding in his or her local areas, and also investigates any mixed finch and sparrow flocks that might be found, or heard about, in the neighbourhood, to determine whether these might contain Tree Sparrows. If Tree Sparrows are found, it would be very helpful to ascertain whether any of them are carrying metal rings (not always especially obvious), as this would probably indicate a Beddington origin. It would be necessary to record the location, the number of birds involved, the duration of their stay, the type of habitat and the nature of the food source.
Two members of both Croydon RSPB Group and Beddington Farm Bird Group - Terry Osborn (t.osborn059@btinternet.com) and John Parish (john@jparish4.wanadoo.co.uk) - will collate your findings. We are not anticipating a huge number of positive results - in fact, there will probably be very few - but it would be helpful if participants could let Terry or John know that they are willing to take part in this survey, so that we have some idea of the likely coverage.
Terry and John guide parties of RSPB members around Beddington Farm (which is off limits to the general public) on one Sunday morning each month. If you or any of your members would like to see the Tree Sparrows at their breeding site, contact one or other of them for the dates of these visits. Incidentally, there are plenty of other interesting birds on the Farm - for instance Jack Snipe and Water Pipit are often present during the winter months, though not guaranteed, of course.
I sincerely hope that some of your members will be able to join us in this important project, and our team greatly looks forward to hearing from them, and perhaps meeting them at Beddington in due course. Please do contact us if you need more information.